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New frontiers in cardiac computed tomography

Session presentations
Non-invasive Imaging: Cardiac Computed Tomography

Low-dose CCTA – Jörg Hausleiter, DE
Over the past decade non-invasive coronary angiography by computed tomography has evolved to a reliable technique to assess coronary artery disease. As the diagnostic performance matured, innovative focus has shifted towards delivering high diagnostic performance while minimization the patient’s exposure to ionizing radiation. In the overview given by dr Jörg Hausleiter from Munich, several of the dose saving techniques were discussed, as well as their impact on image quality. Based on the series of Protection trials the use of lower tube voltage in non-obese patients, prospectively ECG-triggered axial scanning and high-pitch spiral scanning in patients with a low heart rate, resulted in a respectively 31%, 70% and 50% reduction in radiation dose, without a negative effect on image quality. The dose saving potential of new iterative reconstruction techniques is currently being investigated.

CT perfusion – Richard Georg, USA
While the excellent performance to exclude coronary disease has been described extensively, cardiac CT is limited in its ability to assess the hemodynamic severity of obstructive lesions. On one hand this is a consequence of overestimation of the stenotic severity, in part due to image artifacts. Secondly, cardiac CT does not provide hemodynamic significance of the obstructive disease, which is becoming increasingly important for revascularization decision making. Dr Richard Georg from Baltimore discussed the development and clinical performance of stress myocardial perfusion imaging by CT, which represents a new CT application that may overcome the current limitations of CT angiography. Most experience has been gathered with static perfusion imaging during pharmacological vasodilation by acquiring a single CT scan during contrast injection. The attenuation gradient between the inner and outer myocardium is used to differentiate between ischemic and non-ischemic myocardium. Dynamic myocardial perfusion requires acquisition of multiple scans during injection of contrast. From the time-attenuation-curves the absolute myocardial blood flow can then be estimated. The drawback of this method is a generally higher radiation exposure. By either method the specificity of CT angiography can be improved, with anticipated reductions in overall diagnostic cost if implemented. Results of the multicenter CORE 320 study, comparing CTA plus myocardial perfusion imaging with SPECT MPI and invasive angiography, will be presented later during the ESC meeting.

Plaque characterization – Stephan Achenbach, DE
Computed tomography has the unique ability to noninvasively image the atherosclerotic coronary plaque. Dr Stephan Achenbach from Giessen (Germany) discussed the current state of CT plaque imaging. Various plaque characteristics known to be associated with plaque instability, such as stenosis grade, plaque contents (non-calcified versus calcified plaque), outward vessel remodelling, spotty calcification and low plaque attenuation (representing lipid tissue), can be demonstrated by CT with varying accuracy and reproducibility. The severity and extent of obstructive disease on CT has been demonstrated in several registries. Additionally, the extent of atherosclerotic plaque is associated with worse prognosis, although its impact on outcome is of a smaller magnitude compared to lumenal stenosis. The prognostic value of the other previously mentioned characteristics has not been demonstrated in a convincing manner yet. Most importantly, while CT may identify patients at increased risk of acute coronary event, predicting which exact lesions will rupture is currently beyond our reach of cardiac CT. 

Spectral and colour-coded CT – Zahi Fayad, USA
Rontgen attenuation depends on tissue characteristics, but differences between tissues are also affected by the energy level of the interrogating photons. These differences could potentially be exploited to improve the differentiation of tissues on CT images. Dr Zahi Fayad discussed the different techniques for spectral CT imaging and their potential use in clinical imaging. Different vendors are developing techniques for multi-energy imaging. Promising data were presented on K-edge imaging where the specific attenuation characteristics of gold were exploited to selectively image accumulated gold-labelled LDL particles in atherosclerotic plaque in an animal experiment. The advantage of CT over other non-invasive molecular imaging techniques are the short acquisition times and the ability to image the coronary arteries. Introduction of clinical CT scanners with spectral imaging ability are expected over the next few years.




New frontiers in cardiac computed tomography

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.